Generally speaking, the pupil distance of every user is not the same, so in wearable displays and other display products (for example, a head-mounted display) the location of lens must be adjusted to match the pupil distances of different users, in order to facilitate the use of the users and satisfy the personal requirement of the users. FIG. 1 is the schematic illustration of a head-mounted display in the prior art. In FIG. 1, 11 is a front housing of the head-mounted display, and 12 is a lens. When the lens 12 moves leftwardly and rightwardly to adjust the pupil distance, the location of the lens 12 changes and the inside structure of the product is exposed; that is, there is an exposed area. Accordingly, the debris may enter inside of the product through the exposed area and affect the performance and service life of the product, and also affect the appearance of the product.